Vertical tube reactors which use a subterranean U-tube configuration for providing a hydrostatic column of fluid sufficient to provide a selected pressure are known. This type of reactor has been primarily used for the direct wet oxidation of materials in a waste stream but may also be used for pyrolysis, alkylation, hydrolysis and hydrogenation of waste streams. As exemplified by the following patents, reactors of this nature typically comprise a subterranean vertical U-tube reactor system consisting of influent and effluent conduits concentrically arranged for heat exchange, a reaction zone at the bottom of the reactor, and in some cases, a jacket containing heated media for the external heating of the reaction zone, and pipes to supply oxygen or other reactant gases.
Bauer, U.S. Pat. No. 3,499,247 (1969), discloses a method for the wet oxidation of fluid sewage mixed with combustible refuse. Air is pumped into the influent stream at the well head and is pumped directly into the reaction zone from a subterranean compressed air storage chamber. Pressure in the reaction zone produced by the hydrostatic head may be augmented by a pressure regulating device on the effluent stream.
Lawless, U.S. Pat. No. 3,606,999 (1971), discloses a method and apparatus for carrying out oxidation of sewage or aqueous industrial waste. In addition to the U-tube conduits, the apparatus includes gas venting and supply lines, floats and sparges. Air and/or other reactant gases are introduced to the reaction zone through gas lines travelling down the feed pipe (inner conduit) to the sparges. Air released from the sparges and product gases are trapped in the floats, lending buoyancy to the same. The floats are used to support the feed pipe.
Land U.S. Pat. No. 3,464,855 (1969), discloses a method for the aqueous digestion of wood chips. The patent discloses a variation on the U-tube apparatus in that the well installations contain at least three concentric annular passages. Countercurrent coaxial flow paths containing the wood chip solution comprise two of the annular spaces. The coaxial flow paths are in fluid communication with each other at the soaking reservoir at the well bottom. Additional annular spaces, which are not in fluid communication with reactant materials in the countercurrent coaxial flow paths, are described as carrying steam or other heated fluids to serve as a source of external heat to reactant material in surrounding annular spaces. A valve or plate on the reaction product effluent and a reactant influent pump augment the hydrostatic pressure of material within the coaxial pathways.
Titmas U.S. Pat. No. 3,853,759 (1974), discloses a method for pyrolysis, alkylation, hydrolysis and hydrogenation of raw sewage and for the devulcanization of aqueous rubber solutions in an oxygen deficient environment. Titmas has a steam or heat energy line running axially down the center of the liner (inner conduit) to deliver steam or other heated media to the reaction zone. The reaction zone is within an orifice created by annular rings arranged on the inner surface of the liner and the outer surface of the steam line; steam or other heated medium is injected into the orifice to maximize pressure and temperature in the orifice area. The liner conduit may be suspended for the purposes of accommodating metal expansion upon heating.
McGrew U.S. Pat. No. 4,272,383 (1981), discloses a method and apparatus for the wet oxidation of sewage sludge. The first or outer conduit of the U-tube has a closure at its lower end and the second or inner conduit terminates and is suspended above the outer conduit closure. The reaction zone, which is located within the bottom portion of the outer conduit, is temperature controlled by heat exchange with a heated media in a surrounding annular jacket. The apparatus further comprises a pump for pumping influent into the downgoing flow pipe. Oxygen or other reactant gas may be introduced into the downgoing flow passage at the surface and at inlets at spaced intervals below the ground surface level to form enlarged "Taylor" gas bubbles within the influent.
Bain U.S. Pat. No. 4,778,586 (1988), discloses a method and apparatus for the treatment of whole crude to reduce its viscosity and render it more suitable for transportation by pipeline or ship. The U-tube apparatus contains three concentric annular passages. Two of these passages, the downcomer and the riser, contain the hydrocarbon stream and are in fluid communication with each other at the well bottom in the reaction zone. The third annular passage is a jacket located adjacent to portions of the riser and downcomer corresponding to the reaction zone. The heat exchange fluid circulated through the jacket provides the external source of heat used to raise the temperature of the stream to the reaction temperature. Temperature sensors in or above the reaction zone can be used to control the temperature of the jacket heat exchange fluid and minimize formation of coke on conduit walls.
Although the U-tube configuration of the above-cited patents contain inner and outer conduits in heat exchange relationship, annular jackets surrounding the reaction zone with heating media therein and/or air or gas conduits at a variety of locations and depths, none of the patents suggest or disclose an apparatus which would be useful for the direct oxidative heating of a hydrocarbon stream. Further, none of these patents suggest or disclose the central placement and downstream orientation of oxidant nozzles in the stream within the reaction zone, feedback control relationship between oxidant conduit valves, which control the oxidant flow rate to the nozzles, and temperature monitors located in or above the reaction zone.
The present invention involves an apparatus useful in the method described in copending and commonly assigned application, "Improved Viscosity Reduction by Direct Oxidative Heating," Ser. No. 058,878, filed June 5, 1987, now U.S. Pat. No. 4,818,371 incorporated in its entirety herein by reference. Said application describes a method for providing direct oxidative heating of hydrocarbon material to reduce viscosity thereof with reduced coke formation on reactor walls. The method of Ser. No. 058,878 involves direct heating of the hydrocarbon influent stream by dispensing an oxidant centrally in the influent stream, rather than external heating of the influent stream by using heating elements or media in a jacket in heat exchange relationship with the conduit containing the reaction zone. The apparatus of the present invention uses central placement and downstream orientation of oxidant nozzles in the hydrocarbon stream within the reaction zone to achieve the direct oxidative heating described in the process of Serial No. 058,878. The present invention further involves a feedback control mechanism between temperature monitors in or above the reaction zone and oxidant conduit valves.